The micromorph solar cell (stack of amorphous and microcrystalline cells) concept is the key for achieving high efficiency stabilized thin film silicon solar cells. We introduce a device structure that allows a better control of the light in-coupling into the two subcell components. It is based on an asymmetric intermediate reflector, which increases the effective thickness of the a-Si:H by a factor of more than three. Hence, the a-Si:H thickness reduction diminishes the light induced degradation, and micromorph tandem cells with 11.2% initial and 9.8% stabilized efficiencies (1000 h, 50 °C, and 100 mW/cm2) are made on plastic substrates with Tg<180 °C.